As one of optical communication technologies, there has been a large-capacity optical fiber communication system that uses a wavelength division multiplexing (WDM) technology. In such a large-capacity optical fiber communication system that uses a wavelength division multiplexing (WDM) technology, light signals formed by multiple light sources having different wavelengths are transmitted as WDM signals in an optical fiber, which makes large-capacity communication possible. Namely, such WDM signals are transmitted so that signals having wavelengths different from each other are transmitted as signal components of independent channels, respectively, and hence, large-capacity communication is realized. A wavelength division multiplexing communication apparatus that uses such a wavelength division multiplexing technology includes demultiplexers to separate signal components corresponding to respective wavelengths in an optical fiber, and modulators to generate signal components corresponding to the respective wavelengths to be input into the optical fiber.